fix(cardano-services-client): correct blockfrost tx submit request body

it has to be binary, otherwise Blockfrost responds with 400

this bug wasn't caught initially because we're not using
BlockfrostTxSubmitProvider in our e2e test suite

packages/cardano-services-client/src/TxSubmitProvider/BlockfrostTxSubmitProvider.ts

@@ -10,7 +10,7 @@ export class BlockfrostTxSubmitProvider extends BlockfrostProvider implements Tx
   async submitTx({ signedTransaction }: SubmitTxArgs): Promise<void> {
     // @ todo handle context and resolutions
     await this.request<string>('tx/submit', {
-      body: signedTransaction,
+      body: Buffer.from(signedTransaction, 'hex'),
       headers: { 'Content-Type': 'application/cbor' },
       method: 'POST'
     });

packages/cardano-services-client/test/TxSubmitProvider/BlockfrostTxSubmitProvider.test.ts

@@ -1,5 +1,6 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 import { BlockfrostClient, BlockfrostTxSubmitProvider } from '../../src';
+import { HexBlob } from '@cardano-sdk/util';
 import { ProviderError } from '@cardano-sdk/core';
 import { logger } from '@cardano-sdk/util-dev';
 import { mockResponses } from '../util';
@@ -17,7 +18,7 @@ describe('blockfrostTxSubmitProvider', () => {
   describe('submitTx', () => {
     it('wraps error in UnknownTxSubmissionError', async () => {
       mockResponses(request, [['tx/submit', new Error('some error')]]);
-      await expect(provider.submitTx({ signedTransaction: null as any })).rejects.toThrowError(ProviderError);
+      await expect(provider.submitTx({ signedTransaction: HexBlob('abc') })).rejects.toThrowError(ProviderError);
     });
   });
 });